在Urlmon.dll中，有一个名为函数 FindMimeFromData ​​ code>。

In Urlmon.dll, there's a function called FindMimeFromData.

从文档

MIME类型检测，或数据嗅探，是指确定来自二进制数据的适当的MIME类型的过程。最终结果取决于服务器提供的MIME类型标头，文件扩展名，和/或数据本身的组合。一般，只有第一256字节的数据是显著。

MIME type detection, or "data sniffing," refers to the process of determining an appropriate MIME type from binary data. The final result depends on a combination of server-supplied MIME type headers, file extension, and/or the data itself. Usually, only the first 256 bytes of data are significant.

所以，从文件中读取的第一个（最多）256个字节，并把它传递给 FindMimeFromData ​​ code>。

So, read the first (up to) 256 bytes from the file and pass it to FindMimeFromData.